1. Technical Field
The present invention relates to heat dissipation in general, and in particular to a method for managing the speed of a heat dissipating fan for a computer system while harmonizing the processing capability of a processor within the computer system.
2. Description of Related Art
A notebook personal computer (note PC) typically includes many electronic components, such as processors, memories, video cards, etc., which are mounted in high-density within a housing. Such electronic components tend to emit heat during the operation of the note PC, which raises the temperature of the electronic components as well as the housing. A temperature sensor for monitoring temperature is provided within or around certain important electronic components.
Some note PCs may include a heat dissipating (or cooling) fan for dissipating heat by forcing outside air into the housing when the temperature measured by the temperature sensor increases. The heat dissipating fan is configured to be capable of adjusting an amount of heat dissipation by controlling a rotation speed of the heat dissipating fan in multiple steps. The rotation speed of the heat dissipating fan can be increased when the temperature measured by the temperature sensor exceeds a threshold value, or decreased when the measured temperature becomes lower than the threshold value. However, when the rotation speed is controlled in both fast and slow directions based on one threshold value between adjacent rotation speeds, the rotation speed of the heat dissipating fan changes frequently, which can make a noisy sound. Thus, the rotation speed control has hysteresis characteristics, i.e., the note PC controls the rotation speed so that the rotation speed is increased by one step when the temperature of the temperature sensor exceeds a threshold temperature Th1 and is returned to a previous rotation speed when the temperature becomes lower than a threshold temperature Th2 (Th2<Th1).
Among all electronic components mounted within a note PC, a central processing unit (CPU) produces the largest amount of heat. A technology called SpeedStep® can reduce consumption power by decreasing the clock speed and operating voltage of the CPU. In addition, a technology called throttling can operate the CPU intermittently in order to reduce the consumption power. Both of the above-mentioned technologies are able to decrease the amount of heat generation by reducing the processing capability of the CPU. The Advanced Configuration and Power Interface (ACPI) specification distinguishes and defines two cooling methods, namely, active cooling and passive cooling, regarding heat dissipation in computer systems.
Under the active cooling method, the heat dissipating fan is activated first when the temperature of the computer begins to rise, and the processing capability of the CPU is then reduced when the temperature continues to rise after the rotation speed of the heat dissipating fan has reached the maximum rotation speed. Under the passive cooling method, the processing capability of the CPU is initially reduced when the temperature of the computer begins to rise, and the heat dissipating fan is then activated when the temperature continues to rise after the processing capability of the CPU has reduced to the lowest level. The active cooling method places a higher priority on the processing capability, and the passive cooling method places a higher priority on suppressing consumption power and noise of the heat dissipating fan.
On the one hand, note PC users have a desire for a high processing capability so that they can complete their computing tasks in a relatively short amount of time; but on the other hand, they also desire for quietness from their note PC during operation because they prefer not to be annoyed by the heat dissipating fan noise. The amount of heat generation decreases as the processing capability reduces; therefore, it is possible to meet the quietness requirements because temperature can be maintained within a predetermined range even when the heat dissipating fan operates at a low rotation speed. However, the amount of heat generation increases as the processing capability increases; therefore, it is difficult to meet the quietness requirements because the heat dissipating fan needs to be operated at a high rotation speed in order to maintain the temperature. Therefore, the processing capability and the quietness become trade-off factors in control thereof via the internal temperature of the housing.
The heat dissipation method described in the ACPI specification is configured to preliminarily put priority on the processing capability preferential method and the quietness preferential method to be executed in order, or to execute any one of the methods in accordance with the user's selection. In other words, the processing capability preferential method and the quietness preferential method can be selectively executed, or alternatively, when it is too difficult to suppress the temperature rise with only one method, the other heat dissipation method is additionally executed while allowing the heat dissipation method being previously executed to work as much as possible.
When the note PC is used in an interactive mode, there is rarely a case where the processing capability preferential method and the quietness preferential method are to be executed simultaneously. In many cases, therefore, thermal design is performed so that temperature can be maintained by execution of either one of the methods. However, the noise generated from the heat dissipating fan is annoying when heat dissipation is performed by the processing capability preferential method, and the processing capability remains dissatisfactory when heat dissipation is performed by the quietness preferential method. Thus, thermal design is not always satisfactory to a note PC user. Therefore, it is obvious that the maximum level of a note PC user's comfort lies in a heat dissipation system functioning within a range in which the processing capability and the quietness are harmonized, and it is desirable to have a heat dissipation system capable of meeting those requirements.
In thermal design of a heat dissipation system that dissipates heat generated by electronic devices accommodated in a computer using a heat dissipating fan, a rotation speed of the heat dissipating fan is set to the lowest or stop state when a CPU is in an idle state, and the rotation speed of the heat dissipating fan is increased in a stepwise manner when a utilization rate of the CPU increases and an amount of heat generation thereof increases, thereby balancing the amount of heat dissipation and the amount of heat generation so that an inside of a housing is maintained at a predetermined temperature. When a user is performing tasks on the computer, a measurement temperature measured by a temperature sensor varies with the operation state of the system, and the heat dissipating fan operates at a rotation speed which is determined based on a threshold temperature for the measurement temperature. In the above-mentioned example, if the rotation speed control of the heat dissipating fan has hysteresis characteristics, the rotation speed of the heat dissipating fan is increased once the measurement temperature has increased above the threshold temperature Th1, and therefore, it takes a relatively long period of time until the measurement temperature decreases below the threshold temperature Th2 such that the rotation speed decreases.
However, when the changes in the measurement temperature upon application of a typical load to a personal computer other than to a server computer are monitored, it can be noticed that there is rarely a state where temperature that is high enough to increase the present rotation speed of the heat dissipating fan by one step is continuously measured for a long period of time and that a state where the CPU is required to operate with high processing capability occurs sporadically. When the measurement temperature decreases after the rotation speed was increased, although the rotation speed may be decreased between the threshold temperature Th1 and the threshold temperature Th2 from the viewpoint of thermal balancing, since the heat dissipating fan is rotating at one step higher rotation speed, there occurs a difference between the amount of heat dissipation that is based on the actual rotation speed of the heat dissipating fan and the actual amount of heat generation. Moreover, when the temperature exceeds the threshold temperature Th1 for a short period of time, it was noticed that prioritizing the quietness to temporarily decrease the processing capability, thereby maintaining a low rotation speed can provide higher level of comfort to the user than prioritizing the processing capability to increase the rotation speed of the heat dissipating fan.